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DOI: 10.1055/s-2001-14572
Synthesis of 2-Alkylpyrazole-1-oxides: A Facile Access to 1-Alkyl-5-halopyrazoles
Publikationsverlauf
Publikationsdatum:
30. September 2004 (online)
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Abstract
Selective N-alkylation of 1-hydroxypyrazole 1 into the corresponding 2-alkyl-pyrazole-1-oxides 2a-f has been achieved by treatment with alkyl bromides in the absence of base. Subsequent deoxygenation/halogenation into 1-alkyl-5-halopyrazoles 3a-d and 4a-d using phosphorus oxyhalides is described.
Key words
pyrazoles - alkylations - halogenation - deoxygenation - N-oxides
- 1
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References
Note that the numbering in the pyrazole ring changes upon reduction.
8We previously described the preparation of 5-chloro- and 5-bromo-1-benzylpyrazole via selective chlorination/bromination of 2-benzylpyrazole-1-oxide and subsequent deoxygenation using POCl3, for details see ref. 1.
105-Chloro-1-methylpyrazole and 5-chloro-1-benzylpyrazole have been prepared by treatment of the corresponding
5-hydroxy-1-alkylpyrazoles with POCl3 at 155 °C, for details see ref. 12.